1. Field of the Invention
This invention relates to a fabric, in particular for shading purposes, formed of interwoven warp and weft threads based on fluoropolymer plastics, wherein the fabric includes an upper side and an underside having colorings that are different from one another.
2. Discussion of Related Art
It is known to use fabrics made from fluoropolymer plastics, in particular polytetrafluoroethylene (PTFE) for textile constructions, for example, long-span structures. The weights per unit area can be between 300 and 2,200 g/m2, with all conceivable weaves of plain weaves, twill weaves, Panama weaves and special weaves applied. Here, PTFE yarns of 380, 440, 880 and 1,200 dtex are used as single yarns or in twist structures with many different yarn and twist structures. The known PTFE yarns used are, in part, naturally white, or also colored, such as sand-colored, green, blue, red, or yellow.
In 1992 or 1993, for example, twelve large-scale screens in white, each with a size of approx. 600 m2, were installed in the Medina mosque as an outdoor long-span structure using such PTFE weaves.
Pure PTFE is mainly used in fabrics for shading purposes that are exposed to such a high degree of insolation, because, according to current knowledge, only PTFE plastics are subject to almost no degradation of strength in regions of such a high exposure to heat and, in particular, ultraviolet irradiation, and because a life span of 25 years and more can be assumed for such fabrics.
Additionally, with regard to prior art, reference may also be made to German Patent Reference DE 20 2006 008 868 U1.
However, one problem of the known PTFE fabrics is that they exhibit only an inadequate shading effect, in particular if colored white. By increasing the weight per unit area from between 600 to 700 g/m2 to at least 900 g/m2, an improvement could be made but which is not sufficient. Also, the problem of insufficient shading effect is also not solved in a satisfactory manner by augmenting the material with colored PTFE yarns, such as, for example, brown or preferably sand-colored yarns, or producing the material exclusively from them, because although the shading effect is increased, the reflecting properties of a pure white fabric vis-à-vis sunbeams, which is at least as important, is lost at the same time, so that only an insufficient reflection of sunbeams takes place, which makes the temperatures under the shading fabric rise in an undesired manner. In colored blended fabrics, the important characteristic values, namely transmission and absorption, as well as heat transfer of the fabric under insolation, are also unfavorable due to reflection being reduced as compared with a pure white fabric, and an increased temperature is caused under the fabric, which must be avoided under all circumstances.
Also, it is known to form a fabric with different colors on its upper and underside, for example, by printing on one side of the fabric or providing it with a coating that has another coloring different from the fabric itself. However, such a coating is difficult to produce and, with regard to its long-term stability, particularly susceptible to UV irradiation, and it also impairs the flexibility of the fabric, which has a very adverse effect, for example if such fabrics are used in umbrellas, on the foldability of the fabric in case it is not used. This also leads to significantly increased weights per unit area, which in turn cause increased mechanical strain on the fabric and its supporting structure.